Method of making a molded friction lining and bonding same to a brake shoe



1366- 1955 R. w. BISHOP METHOD OF MAKING A MOLDED FRICTION LINING ANDBONDING SAME TO A BRAKE SHOE Original Filed April 21, 1951 2Sheets-Sheet 1 Fig. 3

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METHOD OF MAKING A MOLDED FRICTION LINING AND BONDING SAME TO A BRAKESHOE Original Filed April 21, 1951 2 Sheets-Sheet 2 IN VEN TOR.

Robert W. Bishop His Attorney United States Patent METHOD OF MAKING AMOLDED FRICTION gINING AND BONDING SAME TO A BRAKE HOE Robert \V.Bishop, Fairficld, Iowa, assignor to General Motors Corporation,Detroit, Mich., a corporation of Delaware Original application April 21,1951, Serial No. 222,243. Divided and this application September 16,1953, Serial No. 383,100

2 Claims. (Cl. 154-81) This invention relates to molded segmental brakelinings and a method of making same.

An object of this invention is to provide an improved integral brakelining but having segmental braking surfaces, adapted for use onautomotive vehicles, and an economical and efficient method of makingsame.

This application is a division of application Serial No. 222,243, filedApril 21, 1951.

The braking surface of the integral brake lining of this invention isprovided with a series of intermittently arranged high areas whichengage the rotating brake drum when the brakes are applied and performthe braking effort. These high areas preferably extend the full width ofthe lining and are spaced apart by transversely extending low areas ofsubstantial size which do not engage the brake drum and perform nobraking eifort, hence no eat is generated in these low areas byfriction. These low areas are integral with said high areas and serve toeffectively conduct the heat generated in the high areas to the metalsurface of the brake shoe to which the brake lining is bonded orotherwise fixed in good heat-conducting relation. Thus it is seen thatthe full area of the inside surface of the brake lining is utilized toconduct heat from the lining to the metal brake shoe. These low areasprovide distributed relatively cool portions in the integral lining andthus provide a more uniform heating up and cooling off of the high areasin use. The net etfect of this construction is to provide a moreconsistently uniform heating up and cooling off of the braking surfacelining, and consequently to improve the operating frictioncharacteristics of the brakes. The chief common undesired frictioncharacteristics in present-day molded brake linings are (1) a temporaryreduction or fade out of the coeflicient of friction due to a relativelylarge temperature rise in the braking surface and (2) a subsequentirregular or erratic recovery of the coeificient of friction to or aboveits original value upon subsequent cooling. Obviously any non-uniform orerratic variation or over recovery in the braking coefficient will beconfusing to the driver of the automotive vehicle and seriously afiectssafe driving. A general object of this invention is to provide a brakelining which minimizes the above mentioned undesired characteristics.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown, and wherein:

Fig. l is a side elevation of a brake lining bonded to a metal brakeshoe, made according to this invention.

Figs. 2 to inclusive illustrate a method of manufacture of the brakelining according to this invention.

Fig. 2 is a side elevation of an individual partiallycured lining blankas it is originally made in substantially straight form.

Fig. 3 is a top view of Fig. 2.

Figs. 4 and 5 illustrate how the straight partially cured blank of Figs.2 and 3 is bent into its final curved form,

2,727,845 Patented Dec. 20, 1955 Fig. 4 showing the initial position ofthe parts and Fig. 5 showing the final position of the parts.

In the drawings similar reference characters refer to similar partsthroughout the several views.

Reference numeral 10 designates a straight partially cured blank formaking one lining member. The movable friction compound used in blank 10may be any suitable and well-known compound for this purpose. Suchfriction compounds commonly contain asbestos fiber, heatresistingfriction powders, phenol-formaldehyde resin or other well-knownthermosetting resins, rubber, sulphur, and various filler materials, orvarious combinations of these ingredients. Such plastic compounds may bereadily molded to shape and then cured under heat and pressure tovarious degrees of hardness and rigidity, all in a wellknown manner.

Now according to this invention the blank 10 is first molded from such afriction compound to the section shown in Fig. 2 having a smooth flatlower surface 11 and having alternate high and low areas on itsirregular upper surface. In the form shown in the drawings, the highrectangular areas 15 extend directly across the Width of the elongatedblank 10 and are spaced apart by the low areas 16. Preferably a wideslab of suflicient width to make a plurality of blanks 10 is extrudedand then molded to the section shown in Fig. 2 and partially cured tothe desired degree of hardness under heat and pressure in a pressbetween a flat lower plate and a correspondingly recessed upper plate.Thereafter the individual blanks 10 are cut from the partially curedwide slab by any suitable means by cuts extending crosswise the low andI high areas thereof.

The degree of partial curing of blanks 10 while in the mold should besufficient to determine the final thickness of and provide substantialstrength and rigidity to the relatively thin portions 16 of the blank(and of course still greater strength and rigidity to the relativelythick portions 15 thereof) yet still leave the blank 10 sufficientlyflexible to be bent into the desired final curved form, as by the meansshown in Figs. 4 and 5. Typical curing conditions to provide suchdesired degree of partial cure of a slab from which automobile brakelinings are to be made are about 15 minutes at 280 F. with a pressure of1300 lbs. per sq. inch on the material of the slab.

The partially cured individual blanks 10 may be bent around and bondedto the individual metal brake shoes 29 as follows: The convex outer face21 of the brake shoe is cleaned and preferably finely roughened as bysand blasting, and then coated with a suitable coating ofphenalformaldehyde resin in A stage, or other suitable thermosettingresin. Brake shoe 20 is then set within suitable slots 31 and 32 of aportable baking form as clearly shown in Figs. 4 and 5. A through pin 33accurately locates one end 22 of shoe 20 in slot 31 and the other end 23of brake shoe 20 rests upon abutment 24 within slot 32. The blank 10 iswarmed to a temperature of around 300 F. in order to render it moreflexible and is then bent around and clamped upon the resin-coatedconvex face 21 of the shoe by means of the overlying flexible springsteel band 35. Steel band 35 hinges upon pin 36 at one end thereof andat its opposite end is hinged at pin 37 to handle 38. When the parts arein the position shown in Fig. 4 handle 38 is forced down by hand untilthe two projecting lugs 39 thereon can be hooked under their stationarycooperating notches 40, after which handle 38 is swung downwardly from asubstantially vertical position to the horizontal position shown in Fig.5. Thus the steel band 35 is put under high tension by the leverageaction of lugs 39 fulcruming in their stationary notches 40, and tightlyclamps the brake lining down upon the brake shoe surface 21. If

so desired, the straight blank 1%) may be first bent into itsapproximate final curvature by any suitable means (such as a specialbending mold) before the lining is set upon the convex surface 21 of thebrake shoe. The portable baking form 39, containing the brake liningtightly clamped upon the brake shoe 20, is then baked in an oven tocomplete the cure of the lining material and simultaneously cure thebonding resin coating on surface 21 of the bralaeshoe and so stronglybond the lining over the entire contacting surface of the shoe. Typicalcuring conditions for such final baking operation are three hours bakingat 460 F.

'The above described portable baking fixture has been used heretofore inmaking plain-surfaced brake linings and'therefore this apparatus per seconstitutes no part of this present invention. 1

Operation under normal conditions.

' When the brake linings of this invention are used in an automotivevehicle, the thick portions 15 of course do all the braking workand'hence heat is generated only in said thick portions. The thinportions 16 of the lining normally remain relatively cool when the thickportions 15 heat up and so serve as cool portions spaced along thelength of the lining. These relatively cool portions 16 aid materiallyin conducting heat away from the heated portions 15 and hence reduceboth the rate and degree of temperature rise in portions 15 duringnormal application of the brakes. Thin portions ll: tend to remainrelatively cool since their heat is more quickly dissipated byconduction to the metal brake shoe and to some extent by air circulatingin the open spaces above portions 16. By thus lessening both the rateand degree of temperature rise in'portions 15 the degree of fade out orreduction in the-coefiicient of friction of portions 15 is materiallyreduced.

Operation under abnormal conditions.

Now assume that portions 15 have nevertheless been heated to such a hightemperaturev as to cause a substantial fade out (such as may be causedby descending a mountain). Such a rigorous application of the brakesWill necessarily also heat the thin portions 16 to an unusually hightemperature. When such rigorous application is ended (say at the bottomof the descent) portions 15 Will begin to cool oif and recover from saidsubstantial fade out. If such cooling off is too rapid or not uniformfrom time to time the recovery characteristics of the coefficient offriction of the brakes tend to vary in such an erratic manner as to beconfusing to the driver. With the linings of this invention the heatedthin portions 16 serve to effectively prevent such too rapid rate ofcooling ofportions 15, such as would occur under the above mentionedconditions if portions 16 be omitted entirely.

The thickness of portions 16 is preferably from one half to one third ofthe thickness of portions 15.

While the embodiment of the present invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is as follows:

1. The steps in the method of making a molded friction lining in curvedcylindrical shape and bonded directly to a brake shoe, comprising:molding a thermosetting fibrous friction compound into a substantiallystraight slab having a uniform flat surface on one face thereof andhaving on its opposite face a series of spaced depressed areas and highareas, partially curing said straight slab under heat and pressure,cutting the partially cured straight slab into elongated one-piece brakelining blanks in such direction that said depressed areas extend acrosseach of said blanks, bending each of the partially cured blankslengthwise into arcuate form around a cylindrical metal surface so thatthe spaced high areas of the blank project radially outwardly andtightly clamping said blank throughout its full radial extent thereuponby an overlying flexible metal band which presses upon only saidspacedhigh areas of said blank, then completing the cure or" said liningunder heat while simultaneously bonding said lining to said metalsurface.

2. The steps in the method of making a molded friction lining in curvedcylindrical shape and bonded directly to a brake shoe, comprising:molding a thermosetting fibrous friction compound into a substantiallystraight slab having a substantially even surface on one face thereofand an irregular surface on the opposite face thereof comprising aseries of spaced depressed areas and high areas, partially curing saidslab to such a degree of cure as Will substantially determine the finalthickness of said high areas but will still permit said blank to be bentinto the curvature of the final brake lining, cutting said slab intoelongated individual brake lining blanks, bending each of the elongatedpartially cured blanks lengthwise into its final arcuate form around acylindrical metal surface so that the spaced high areas of the blankproject radially outwardly and tightly clamping said blank throughoutits full radial extent thereupon by an overlying fiexible metal bandwhich presses upon only said spaced high areas of said blank, thencompleting the cure of said lining under heat while simultaneouslybonding said lining to said metal surface.

References Cited in the file of this patent UNITED STATES PATENTS

1. THE STEPS IN THE METHOD OF MAKING A MOLDED FRICTION LINING IN CURVEDCYLINDRICAL SHAPE AND BONDED DIRECTLY TO A BRAKE SHOE, COMPRISING:MOLDING A THERMOSETTING FIBROUS FRICTION COMPOUND INTO A SUBSTANTIALLYSTRAIGHT SLAB HAVING A UNIFORM FLAT SURFACE ON ONE FACE THEREOF ANDHAVING ON ITS OPPOSITE FACE A SERIES OF SPACED DEPRESSED AREAS AND HIGHAREAS, PARTIALLY CURING SAID STRAIGHT SLAB UNDER HEAT AND PRESSURE,CUTTING THE PARTIALLY CURED STRAIGHT SLAB INTO ELONGATED ONE-PIECE BRAKELINING BLANKS IN SUCH DIRECTION THAT SAID DEPRESSED AREAS EXTEND ACROSSEACH OF SAID BLANKS, BENDING EACH OF THE PARTIALLY CURED BLANKSLENGTHWISE INTO ARCUATE FORM AROUND A CYLINDRICAL METAL SURFACE SO THATTHE SPACED HIGH AREAS OF THE BLANK PROJECT RADIALLY OUTWARDLY ANDTIGHTLY CLAMPING SAID BLANK THROUGHOUT ITS FULL RADIAL EXTENT THEREUPONBY AN OVERLYING FLEXIBLE METAL BAND WHICH PRESSES UPON ONLY SAID SPACEDHIGH AREAS OF SAID BLANK, THEN COMPLETING THE CURE OF SAID LINING UNDERHEAT WHILE SIMULTANEOUSLY BONDING SAID LINING TO SAID METAL SURFACE.